System and method for un-interrupted operation of communications during interference

ABSTRACT

Methods and systems to substantially eliminate effects of EMI burst noise in an Ethernet system are provided herein. The method includes the step of computing and storing filter coefficients configured to adapt to a range of EMI frequencies. The method further comprises the step of receiving a signal and detecting EMI and frequency of the EMI in the received signal. The method further comprises selecting filter coefficients corresponding to the determined frequency of the detected EMI and adjusting a frequency response of one or more filters using the selected filter coefficients so as to substantially eliminate effects of the EMI in the received signal. The method further includes the step of sending filter coefficients to a link partner corresponding to the frequency of the detected EMI.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/257,982 filed on Nov. 4, 2009, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This application is generally related to detecting and eliminatingeffects of interference in communication systems.

2. Background Art

Interference signals such as Electromagnetic Interference (EMI) ofteninclude narrowband signals centered at one or more frequencies. Thefrequency can be as low as a few MHz and as high as a few GHz. HAMradios, Walkie-Talkies and emergency vehicle sirens are examples ofdevices that generate EMI that impedes communications. These types ofsignals are transient and may cause a link drop or un-acceptable BitError Rate (BER) in a communication system. For example, a 10 GBASE-Tsystem is sensitive to EMI signals that fall in its operating band ofnear DC to ˜400 MHz. 10 GBASE-T systems are more sensitive to EMIbecause the communication channel between a link and link partner in a10 GBASE-T system is typically operating very close to the channelcapacity to allow for a high data rate. In the event of EMI bursts, suchsensitive channels are known to drop a communication link between a linkand a link partner.

Method and systems are needed to overcome the above mentioneddeficiences.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1A illustrates an exemplary bi-directional communication system.

FIG. 1B further illustrates the bi-directional communication system ofFIG. 1A.

FIG. 2 illustrates a Physical Layer (PHY) transceiver.

FIG. 3 illustrates a PHY transceiver to detect and substantiallyeliminate effects of EMI to allow for un-interrupted communicationaccording to an exemplary embodiment.

FIG. 4A illustrates a graph of a frequency response of a Feed ForwardEqualizer (FFE).

FIG. 4B illustrates a graph of Power Spectral Density (PSD) of EMI.

FIG. 4C illustrates a graph of a frequency response, of a feed forwardequalizer, that has been modified to substantially eliminate the effectsof EMI on a received signal according to an exemplary embodiment.

FIG. 5A-C illustrates an example sequence of bit patterns transmitted toa link partner to indicate whether EMI is present or absent.

FIG. 6 illustrates an example flowchart that depicts steps performed bya PHY layer receiver to substantially eliminate EMI according to anexemplary embodiment.

FIG. 7 illustrates an example flowchart that depicts steps performed bya PHY layer upon receiving indication of EMI from a link partneraccording to an exemplary embodiment.

FIG. 8 illustrates an example flowchart that depicts steps performed bya PHY transceiver to substantially eliminate effect of EMI from areceived signal according to an exemplary embodiment.

The present invention will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers mayindicate identical or functionally similar elements.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A illustrates an exemplary bi-directional communication system.Communication system 100 includes a link 102 and a link partner 104coupled by conductor pairs 106 a-n.

In an embodiment link 102 and link partner 104 are part of an Ethernetsystem, for example a 10 GBase-T Ethernet system. Each of conductorpairs 106 may be a balanced twisted pair conductor. It is to beappreciated that embodiments presented herein are not limited toEthernet systems or twisted pair conductors and are applicable to anycommunication system. Link 102 and link partner 104 may be computingdevices such as a personal computers, laptops, mobile communicationdevices or servers such as internet servers. The term “link partner”denotes the device on the other end of a communication link. Forexample, link 102 is the “link partner” of link partner 104 and linkpartner 104 is the “link partner” of link 102. Link 102 and link partner104 are described further below with respect to FIG. 1B.

FIG. 1B further illustrates the bi-directional communication system ofFIG. 1A. Each of link 102 and link partner 104 includes an interface114, PHY 108, hybrid 110 and a computing device 116 that has processor118 and a memory 120.

In link 102, computing device 116 a is coupled to interface 114 a. PHYs108 a-d are coupled to interface 114 a. PHYs 108 a-d are coupled tocorresponding hybrids 110 a-d. Hybrids 110 a-d are coupled to hybrids110 e-h in link partner 104 via conductors pairs 106 a-d. Hybrids 110e-h are coupled to corresponding PHYs 108 e-h. PHYs 108 e-h are coupledto interface 114 b. Interface 114 b is coupled to computing device 116 bwhich includes processor 118 b coupled to memory 120 b.

High level application layers run on, for example processor 118 ofcomputing device 116. Interface 114 couples PHY 108 to higher levellayers such as a media access control (MAC) layer and application layersthat run on computing device 116. PHY 108 (also referred to as a “PHYtransceiver” herein) couples a link layer such as the MAC layer tophysical media such as conductor pairs 106. In an example, embodimentspresented herein are implemented in PHY 108. PHY 108 is described infurther detail with respect to FIGS. 2-3 below. Hybrid block 110 ensuresthat a receiver 212 (see FIG. 2) in PHY 108 does not see what issimultaneously transmitted over each conductor pair 106 by a transmitter200 (see FIG. 2) in full-duplex mode. In other words, each hybrid block110 separates the transmit signal from the receive signal for each PHY108.

Communication between link 102 and link partner 104 may be hindered byelectro magnetic interference (EMI) 112. In previous versions ofEthernet systems that use copper PHYs, such as 10/100/1000 BASE-Tsystems, the channel capacity is much higher than the system data rate.These systems were relatively robust in the presence of EMI. However,EMI may be especially detrimental to communications in a 10 GBASE-TEthernet systems. Data rates in typical 10 GBASE-T systems are veryclose to available channel capacity, thereby significantly reducing thesignal-to-noise ratio (SNR) margin compared to SNR margins of10/100/1000 BASE-T systems. Current 10 GBASE-T systems easily drop acommunications link in the presence of even moderate EMI signals such asa signal generated by a Walkie-Talkie.

Network providers typically impose a block error rate stipulation oncommunication systems. For example, for Ethernet systems, networkproviders typically tolerate a block error rate of 10⁻² in the presenceof EMI, provided that a communication link between link 102 and linkpartner 104 is not dropped. The block error rate is computed using amoving window of 1 second by counting the number of blocks in errorduring a moving 1 second window. In this example, the percentage ofblocks in error should not be more than 1%. Considering thisstipulation, a communication system can be completely in error for 1% ofthe first 1 second window following the onset of EMI, and still bewithin the guidelines set for Ethernet systems, if in the remaining 99%of blocks are error free. Therefore, the first 10 ms after the onset ofEMI can be used to detect and take corrective action to suppress theEMI. Errors which occur during the first 10 ms will not violate theabove stipulation of acceptable system performance in the presence ofEMI.

Effects of steady state narrowband EMI may be eliminated by usingsufficiently long, properly tuned, forward and feedback equalizers.However, these equalizers do not suppress interference of a transientnature such as an EMI spike (see for example EMI spike 414 in FIG. 4B).Specifically, during the transition from no EMI present to EMI present,or during the transition from EMI at one frequency to EMI at a differentfrequency, EMI spikes such as spike 414 are observed. The interferencedue to EMI spikes is typically not suppressed until equalizers in PHYtransceivers have had time to adapt. However, during the time requiredto adapt to an EMI spike, a receiver is very likely to receive anunacceptable number of errors and hence drop a communication link, forexample, a communication link between link 102 and link partner 104.Decision directed adaptation may result in a high error rate that cancause an equalizer convergence failure. Furthermore, if a high errorcondition persists for an extended period of time, higher level layersmay also drop the communication link. What is needed is a scheme torapidly detect the onset of EMI and EMI spikes and robustly determinethe appropriate equalization response in the presence of the EMI to keephigher level layers from dropping the communication link. Embodimentspresented herein detect EMI spikes and adapt a system to account for theeffects of the EMI spike within the pre-determined time period (e.g. atime period of 10 ms) that is acceptable to the relevant communicationsstandard in use. It is to be appreciated that the block error rate andwindow of time to detect and adapt to EMI is a design requirement andmay differ based on implementation and the type of communication system.It is to be appreciated that the embodiments presented herein areapplicable to any communications system.

To overcome the long felt need for a robust communication system thatcan detect and eliminate effects of EMI, the inventors have provided theembodiments presented herein to detect and eliminate the effects of EMIburst noise. According to an embodiment, prior to the onset of EMI at agiven frequency (or set of frequencies), optimal filter coefficients andequalizer responses are determined for a range of assumed EMIfrequencies. The frequency response of equalizers is based on filtercoefficients that are pre-computed for a range of frequencies and may bestored in a table (e.g. table 1 below) of equalized frequency responses.In an embodiment, the range of EMI frequencies for which filtercoefficients are computed within a selected range of the bandwidth ofthe communication system, for example ˜0 MHz-˜400 MHz for 10 GBASE-TEthernet. This is because EMI outside of the operational band may notaffect performance of the communication system considerably. Each tableentry may include filter coefficients or other equalizer parameters forthe physical channel for multiple EMI frequencies. In alternateembodiments equalizer responses and filter coefficients are computedon-the-fly or in real time. The time required to compute equalizers canbe significantly reduced using an analytical channel inversion basedapproach. The table of coefficients and equalizers may be updated fromtime to time to account for variations in the physical channel (e.g.variations in conductor pairs 106).

Upon detection of EMI and its frequency, the frequency response of oneor more filters is modified using coefficients in the table thatcorresponds to the closest frequency to the detected EMI frequency. If aportion of the channel equalization is in the link partner's transmitter(as is the case for 10 GBASE-T), then the frequency of detected EMIand/or filter coefficients are communicated to the link partner using asignaling scheme which is robust in the presence of un-suppressed EMI.Embodiments presented herein are substantially implemented at PHY layer108 and are further described below with respect to FIGS. 2 and 3.

FIG. 2 illustrates an exemplary PHY 108. PHY 108 includes a transmitter200 and a receiver 212.

The input of transmitter 200 is coupled to interface 114 and the outputis coupled to hybrid 110. The input of receiver 212 is coupled to theoutput of hybrid 110 and the output of receiver 212 is coupled to theinput of interface 114. Transmitter 200 includes framer and scrambler202, low-density-parity-check (LDPC) encoder 204, pre-coder 206,digital-to-analog converter (DAC) 208 and line driver 210. The input ofLDPC encoder 204 is coupled to the output of framer and scrambler 202.The input of pre-coder 206 is coupled to the output of LDPC encoder 204.The input of digital-to-analog converter 208 is coupled to the output ofpre-coder 206. The input of line driver 210 is coupled to the output ofdigital-to-analog converter 208. The input of hybrid 110 is coupled tothe output of line driver 210. In an example, transmitter 200 receivesdata for transmission from application layers running on computingdevice 116.

In operation, an application layer program running on processor 118sends data for transmission via link 274 to interface 114. Interface 114sends data 272 to framer and scrambler 202. Framer and scrambler 202scrambles data 272 and appends frames, based on the communicationprotocol in use, to data 272 to generate framed data 236. LDPC encoder204 generates and appends parity bits to framed data 236 and generatesencoded data 238. Pre-coder 206 pre-shapes encoded data 238 to accountfor Inter Symbol Interference (ISI) during transmission such that areceiver at a link partner does not experience channel effects due toISI. In an example, pre-coder 206 is a Tomlinson-Harashima pre-coder.Pre-coder 206 pre-shapes encoded data 238 to generate pre-shaped signal240. Digital-to-analog converter 208 converts pre-shaped signal 240 intoanalog signal 242. Line driver 210 amplifies analog signal 242 togenerate transmission signal 244. Hybrid 110 separates transmit signal244 from receive signal 246.

Receiver 212 includes de-framer and de-scrambler 214, LDPC decoder 216,decision feedback equalizer (DFE) 220, slicer 218, feed forwardequalizer (FFE) 222, echo canceller 230, 3× Near End Cross Talk (NEXT)canceller 232, analog-to-digital converter 224, receive filter 226 andvariable gain amplifier (VGA) 228. Variable gain amplifier 228 receivesdata on conductor pair 106 via hybrid 110. The input of receive filter226 is coupled to the output of variable gain amplifier 228. The inputof analog-to-digital converter 224 is coupled to the output of receivefilter 226. The input of feed forward equalizer 222 is coupled to theoutputs of echo canceller 230, 3× NEXT canceller 232 andanalog-to-digital-converter 224. The input of slicer 218 is coupled tothe outputs of decision feedback equalizer 220 and feed forwardequalizer 222. The input of LDPC decoder 216 is coupled to the output ofslicer 218. The input of de-framer and descrambler 214 is coupled to theoutput of LDPC decoder 216. The input of interface 114 is coupled to theoutput of de-framer and de-scrambler 214. Receiver 212 sends datareceived from a link partner to computing device 116 for processing.Receiver 212 also includes Least Means Squared Unit 234 that is coupledto slicer 218, analog-to-digital converter 224, feed forward equalizer222, decision feedback equalizer 280, echo canceller 230 and 3× NEXTcanceller 232.

In operation, receiver 212 receives signal 246 from conductor pair 106via hybrid 110. Variable gain amplifier 228 amplifies received signal246 to generate amplified signal 248. Receive filter 226 filtersamplified signal 248 to remove noise and generate filtered signal 250.Analog-to-digital converter 224 converts filtered signal 250 intodigital signal 252. Echo canceller 230 generates echo cancellationsignal 254, based on pre-shaped signal 240, to remove interferenceintroduced due to a signal 244 that is transmitted by transmitter 200.3× NEXT canceller 232 generates 3× NEXT cancellation signal 256 tocancel interference effects of transmissions and receptions by adjoiningconductors pairs. For example, transmissions and receptions on conductorpairs 106 b-d will interfere with any signal received on conductor pair106 a. These interferences are accounted for by 3× NEXT cancellationsignal 256. Echo cancellation signal 254 and 3× NEXT cancellation signal256 are combined to form cancellation signal 258. Cancellation signal258 is combined with digital signal 252 to form adapted signal 260 whichis fed into feed forward equalizer 222. Feed forward equalizer 222cancels pre-cursor ISI in adapted signal 260 to generate shaped signal262.

During startup, decision feedback equalizer 220 outputs feedback signal266 that is based on sliced signal 264 or a training sequence 292.Decision feedback equalizer 220 removes post-cursor ISI from slicedsignal 264. The DFE coefficients 280 are generated by least-mean-square(LMS) unit 234. In an embodiment, decision feedback equalizer 220 isoperational only during startup and is deactivated after startup. DFEcoefficients 280 are then used by the pre-coder 206 on a link partnerside to remove post-cursor ISI. DFE coefficients 280 can be applied topre-coder 206 because the DFE 220 and pre-coder 206 are mathematicallyequivalent.

Feedback signal 266 is combined with shaped signal 262 to generateslicer input signal 263. Slicer input signal 263 is sliced by slicer 218which separates signal 263 into multiple digital levels and generatessliced signal 264. LDPC decoder 216 uses parity bits in sliced signal264 to correct for errors and strips the parity bits from sliced signal264 to form decoded signal 268. Deframer and descrambler 214 descramblesdecoded signal 268 and extracts data from frames in decoded signal 268to generate data signal 270. Data signal 270 is transmitted to processor118 in computing device 116 for processing via interface 114.

Receiver 212 also includes LMS unit 234. LMS unit 234 receives errorsignal 246, pre-shaped signal 240 and digital signal 252 as inputs. Inan embodiment a data signal other than digital signal 252 may be used.In an example, error signal 246 is the difference between sliced signal264 and slicer input signal 263. In other embodiments error signal maybe another signal. LMS unit 234 generates feed forward equalizer (FFE)coefficients 278, decision feedback equalizer (DFE) coefficients 280,echo canceller coefficients 282, and 3× NEXT canceller coefficients 284.Feed forward equalizer coefficients 278, decision feedback equalizercoefficients 280, echo canceller coefficients 282, and 3× NEXT cancellercoefficients 284 determine the frequency response of feed forwardequalizer 222, decision feedback equalizer 280, echo canceller 230 and3× NEXT canceller 232 respectively. As will be described further belowwith respect to FIG. 3, embodiments presented herein may: (1)pre-compute and store feed forward equalizer coefficients 278 anddecision feedback equalizer coefficients 280 for multiple potential EMIfrequencies prior to the actual onset of EMI; (2) detect EMI and adaptFFE and DFE (for example adapt FFE and DFE coefficients); (3) signalpresence of EMI to a link partner; and (4) send DFE coefficients and/orEMI frequency to a link partner.

FIG. 3 illustrates an example PHY 108′ according to an exemplaryembodiment. PHY 108′ includes, in addition to the elements describedabove with respect to PHY 108 of FIG. 2, a tone detector 302 and adirect digital frequency synthesizer (DDFS) 310.

1. Pre-Computing Filter Coefficients

In an embodiment, FFE coefficients 278 and DFE coefficients 280 arecomputed by the LSM unit 234 during startup before the onset of EMI fora range of frequencies and stored in a memory (not shown) in the LMSunit 234 or in memory 120. In another embodiment, FFE coefficients andDFE coefficients are computed by processor 118 during startup before theonset of EMI for a range of frequencies and stored in memory 120, or anyother available memory. In a further embodiment, FFE coefficients 278and DFE coefficients 280 are computed in real time by LMS unit 234 orprocessor 118 corresponding to a determined EMI frequency.

In an example, FFE coefficients 278 and DFE coefficients 280 arecomputed for multiple frequency bins. If F is the frequency bandwidth ofa communication system and N is the desired number of frequency bins forEMI, then the width (W) of each frequency bin is W=F/N. For example, ina 10 GBase-T system with a bandwidth of 400 MHz, if 128 bins are desiredthen the width W of each bin is given by 400/128=3.125 MHz. The width Wof each frequency bin in this case is much wider than the bandwidth ofany potential EMI signal. In embodiments presented herein a frequencyresponse of a FFE 222 and DFE 280 are modified upon detection of EMI toinclude a notch with a width of a single or multiple bins to notch outany detected EMI and substantially eliminate effects of the EMI from thereceived signal. The DFE and FFE coefficients may be selected based onthe frequency of the detected EMI. For example, if EMI is detected at151 MHz, FFE and DFE coefficients with a notch in the frequency binranging from 150 MHz to 153.125 MHz may be selected to notch out theEMI.

In an embodiment, during system startup and prior to the onset of EMI,FFE coefficients and DFE coefficients are computed assuming that an EMIsignal is located at the center of a first frequency bin. Based on thisassumption, FFE coefficients and DFE coefficients are computed, forexample using an analytical channel inversion method, and stored inmemory, for example, memory 120. Then, assuming that EMI is located atthe center of the second frequency bin, FFE coefficients and DFEcoefficients are computed and also stored in memory. This process isrepeated for each bin. The computed FFE coefficients and DFEcoefficients may be stored in a table indexed by the EMI frequency binsas shown below in table 1.

TABLE 1 EMI Frequency bins DFE coefficients FFE Coefficients 0 to 3 MHzA B 3 to 6 Mhz C D . . . . . . . . . 150 to 153.125 L M . . . . . . . .. 396.875 to 400 Mhz X Y

In Table 1 above, the width of the frequency bins is uniform. It is tobe appreciated that alternatively, embodiments presented herein are alsoapplicable when the width of frequency bins are non-uniform.

In Table 1 above, each entry represents coefficients of a filter. Forexample, A may represent 16 coefficients that are required to adapt aDFE 220 to notch-out EMI in the range of 0 to 3 MHz. The number ofcoefficients are the same as the number of taps of the filter. SimilarlyB may represent, for example, 128 coefficients that are required toadapt a FFE 222 to notch-out EMI in the range of 0 to 3 Mhz. In anexample, if the number of bins is 128 and if the number of coefficientsis 144 per bin (128 for FFE 222 and 16 for DFE 220) then for N=128,coefficient storage require at most 4*128*(128+16)=73,728 words. Onepossible way to reduce the required memory is to save only DFEcoefficients and when the frequency of EMI signal 112 is detected,compute/adapt the FFE coefficients based on the known DFE coefficientscorresponding to the detected EMI frequency. In this example, therequired memory would be reduced to accommodate 4*128*16=8,192 words. Inorder to account for timing drift or other changes in the channelbetween link 102 and link partner 104, FFE coefficients and/or DFEcoefficients may be re-computed periodically.

2. EMI Detection, FFE and DFE Adaptation

Based on one or more of digital signal 252, adapted signal 260 andsliced signal 264, tone detector 302 detects electromagneticinterference 112 and the frequency of the electromagnetic interference112. Tone detector generates signal 304 to indicate a frequency of thedetected EMI 112. In an embodiment, an LDPC block has duration of 320ns. Therefore, in 1 ms, there are 3,125 LDPC blocks present which allowsfor enough time for detection of EMI and determination of a frequency ofthe EMI within the 10 ms window described above.

If EMI 112 is very strong, then tone detector 302 uses power spectraldensity (PSD) of digital signal 252 to estimate the PSD of the detectedEMI and its approximate frequency. To determine PSD of digital signal252, a Fast Fourier Transform (FFT) of the digital signal 252 iscomputed. The FFT is averaged to account for noise. The magnitude of theFFT is the PSD of digital signal 252. A transient EMI signal istypically detected as a spike in the PSD. For example, as shown in FIG.4B, transient EMI may produce a spike 414 that can be distinguished fromthe PSD of digital signal 252.

If EMI 112 is of moderate strength, then adapted signal 260 which isgenerated after echo cancellation and 3× NEXT cancellation may be used.PSD of adapted signal 260 is examined by tone detector 302 to determinepresence of EMI and it approximate frequency.

If the EMI 112 is relatively weak, then a PSD of the difference betweensliced signal 264 and slicer input signal 263 may be used by tonedetector 302 to detect the presence of EMI and determine its frequency.

In an embodiment, upon detecting EMI, tone detector 302 generates asignal 304 that indicates frequency of the EMI signal. Based on thedetected frequency of the EMI, FFE coefficients 278, and DFEcoefficients 280 corresponding to the detected frequency are selectedfrom the pre-computed FFE coefficients and DFE coefficients stored inmemory 120. The selected FFE coefficients are applied to feed forwardequalizer 222. The selected DFE coefficients 280 are sent to linkpartner 104 as will be described below. These DFE coefficients 280 areto be used by the pre-coder 206 of link partner 104 in order tocommunicate reliably in, for example, Double Squared Quadratureamplitude modulation (DSQ128) mode.

Consider an example where feed forward equalizer 222 has a frequencyresponse 400 as shown in FIG. 4A. The X axis in FIG. 4A is frequency andthe Y axis is the magnitude of the frequency response 400. FIG. 4B showsa graph of electromagnetic interference 408. The X axis in FIG. 4B isfrequency 412 and the Y axis is power spectral density (PSD) of the EMI.In this example, an EMI spike 414 is detected at a frequency 406. InFIG. 4C, the adapted frequency response 400′ of feed forward equalizer222 includes a notch 416 at frequency 406 to notch out effects of EMIsignal 414 from a received signal. In an embodiment, notch 416 is theresult of modification of FFE coefficients 278. In an alternateembodiment, notch 416 is the result of a notch filter (not shown)applied to shaped signal 262. The width 418 of the notch 416 infrequency response 400′ of feed forward equalizer 222 is equal to thewidth W of the frequency bin that covers frequency 416. In the aboveexample, if frequency 416 is 151 MHz, width 418 of the notch 416 isapproximately 3.125 MHz ranging from 150 MHz to 153.125 MHz. Since a 10GBASE-T signal is wideband, notching out one or even a small number ofbins from a frequency response of FFE 222 does not significantly reducethe received signal power.

The notch 416 in frequency response 400 may introduce ISI. As describedfurther below, to account for this ISI, DFE coefficients 280corresponding to the frequency bin of frequency 406 are transmitted to alink partner 104. For example, link 102 may transmit DFE coefficients tolink partner 104 that correspond to the frequency bin that covers EMIfrequency 406. Link partner 104 applies the DFE coefficients 280 to itspre-coder 206 since DFE 220 and pre-coder 206 are mathematicallyequivalent as described above. The modified response of pre-coder 206removes ISI due to notch 416.

In an example, if the EMI source changes location (e.g a person walkingwith a walkie-talkie), the EMI frequency stays constant and hence thenotch 416 is still applicable. In the case of Doppler Effect (forexample in the case of EMI from an ambulance siren) changes the EMIfrequency, the change is very small compared to the width W of thefrequency bin for the notch 416. For example if the frequency of the EMIchanges from 151 MHz to 150 MHz or 152 MHz, the notch 416 with a widthof 3.125 MHz will still remove the EMI. Thus, a system adapted for onespecific EMI location offers EMI suppression even when the EMI sourcechanges location.

In an embodiment, the magnitude of notch 416 may be adjusted based onmagnitude of EMI spike 414. For example, if EMI spike 414 is higher,then a proportionally deeper notch 416 may be used and vice versa.

In an embodiment, if previously detected EMI is not observed again atthe same frequency 406 for a pre-determined period of time then thenotch 416 corresponding to frequency 406 may be removed to preventunnecessary degradation of channel SNR.

3. Alerting a Link Partner to Presence of EMI

In an embodiment, a pre-determined sequence of bits may be used to alerta link partner to the presence of EMI. For example, the 10 GBASE-Tstandard defines an unused 3.125 Mbps side channel to the 10 Gbps datachannel. This side channel includes an “auxiliary bit” in each LDPCblock. Auxiliary bits of consecutive LDPC blocks may be used to send amessage to the link partner to indicate presence or absence of EMI. Forexample, an alternating sequence of “1010” in the auxiliary bits of fourconsecutive LDPC blocks might indicate absence of EMI. Four LDPC blocksmay be considered to form a “frame.” To indicate presence of EMI to alink partner, a link changes the auxiliary bit such that the alternatingsequence of “1010” does not occur in 2 out of 3 consecutive frames. 2out of 3 frames (i.e. 12 consecutive LDPC blocks) are used because it isexpected that in the presence of EMI most of the bits including theauxiliary bit may be in error. Using 2 out of 3 frames provides extrarobustness in the signaling mechanism in case of auxiliary bit errors.For example, in FIG. 5A, the alternating pattern is present in all 3frames indicating to a link partner that no EMI is present. In FIG. 5B,the alternating pattern is not present in frame 2. However, this is notconsidered an indication of EMI since only 1 out of 3 frames are missingthe alternating pattern. The broken pattern may be because of the rareoccasion where the auxiliary bit is itself in error. However, theprobability that 2 or more auxiliary bits to be in error in 2 out of 3consecutive frames in the absence of EMI is extremely low. For example,in FIG. 5C, frames 2 and 3 are missing the alternating patternindicating presence of EMI. Auxiliary bit alternation is used since itdoes not require both ends of a link to be synchronized in terms ofauxiliary bit values. It is to be appreciated that other patterns, andbits other than the auxiliary bit may be used to indicate the presenceto EMI to a link partner.

In a further embodiment, direct digital frequency synthesizer 310generates a signal 312 that signals presence of EMI to a link partner.For example, direct digital frequency synthesizer 310 may generate andtransmit a sine wave of a pre-determined magnitude and frequency toindicate the presence of EMI to a link partner.

4. Transmit Newly Computed, Adapted, or Presorted Coefficients to a LinkPartner

In addition to indicating presence of EMI, a link 102 may also transmitDFE coefficients to its link partner 104. The DFE coefficients are usedby the pre-coder 206 of the link partner 104 to account for EMI 112 andthe adapted frequency response of FFE 222 of link 102.

When EMI is coupled to the system, DFE coefficients transmitted to alink partner may not reliably reach the link partner if DSQ128 mode isin use. Therefore, in an embodiment, during the presence of EMI, bothlink 102 and link partner 104 switch to a Pulse-Amplitude Modulation 2(PAM2) signaling mode which is more robust in the presence of EMI. Sincethe size of DFE coefficients that need to be exchanged is relativelysmall, the link partners may use a low complexity code, such as arepetition code. For example, assuming that 16 DFE coefficients are tobe transmitted to the link partner with each code being 8 bits wide, thetotal data to be transmitted is 128 bits. Each LDPC block includes 256samples taken at 800 MHz. If each sample represents a PAM2 signal, thenin each LDPC frame we can transmit 256 bits. If a repetition code thatuses 10 repetitions is used, then 5 LDPC frames are needed to transmitthe DFE coefficients which will take 1.6 μs. This time to transmit theDFE coefficients is well within the 10 ms window described above todetect and correct the effects of EMI in system 100. In anotherembodiment, LDPC coding may be used in addition to repetition coding tofurther increase reliability of transmission.

In another embodiment, processor 118 in link 102 may transmit DFEcoefficients corresponding to the determined frequency of the detectedEMI to a link partner 104 by encoding the DFE coefficients 260 in aHigh-level Data Link Control (HDLC) packet. In another embodiment, onlythe frequency of the detected EMI is relayed to the link partner 104 byencoding the frequency in an HDLC packet. The link partner 104 uses theencoded frequency of the EMI to generate the DFE coefficientscorresponding to the EMI frequency. In another embodiment, link partner104 uses the frequency received from the link 102 to index apre-computed table, such as table 1, to determine the DFE coefficientscorresponding to the received frequency. Link partner 104 applies DFEcoefficients to pre-coder 206 to adjust its response to account for EMI112 and the adjusted response of FFE 222 and DFE 220 of link 102.

In a further embodiment, the frequency of signal 312 generated by directdigital frequency synthesizer 310 is of the same frequency as that ofthe detected EMI, thereby indicating the EMI frequency to the linkpartner. In yet another example, the magnitude of the sine wave signal312 may indicate the magnitude of EMI 112. Link partner 104 may use thefrequency of the sine wave signal 312 to select and/or compute thecorresponding DFE coefficients. The magnitude of signal 312 may be usedby link partner 104 to proportionally adapt the magnitude of DFEcoefficients that are applied to pre-coder 206.

After exchanging the DFE coefficients, link partners use theadapted/computed FFE coefficients 278 and received DFE coefficients 280.It is expected at this stage that only 1-2 ms of the total 10 ms windowallowed for less than 1% packet error rate has been used. The remainingportion of the 10 ms window may be used to: adapt/fine tune the 3× NEXTcanceller coefficients 284, adapt/fine tune echo canceller 282, and finetune other components of PHY 108′ before returning to DSQ128 mode oftransmission. In an example, upon detection of the presence of EMI, alladaptive filters (for example, echo canceller 230 and 3× NEXT canceller232) as well as timing recovery integral loops may be stalled or frozenand released after DFE coefficients are exchanged in order to speed upthe convergence of the adaptive filters.

The DFE coefficient transmission to link partner 104 can also be done byhigher layers. For example, Link Layer Discovery Protocol (LLDP) can beused to send and maintain the computed Table 1 of DFE coefficients fromtime-to-time to the link partner 104 when there is no EMI. The advantageof this method of coefficient update is that the mode of transmissiondoes not have to be switched from DSQ128 to PAM2 and back to DSQ128 totransmit DFE coefficients in the presence of EMI. In this example, it issufficient to transmit to link partner 104, either the frequency of EMI,or an index into a table that includes DFE coefficients corresponding todifferent EMI frequencies.

FIG. 6 illustrates an example flowchart 600 depicting steps performed bya PHY layer transceiver to substantially eliminate EMI according to anexemplary embodiment. Flowchart 600 will be described with continuedreference to the example operating environment depicted in FIGS. 1-5.However the flowchart is not limited to these embodiments. Note thatsome steps shown in flowchart 600 do not necessarily have to occur inthe order shown.

In step 602, filter coefficients are pre-computed and stored prior tothe onset of EMI. For example, processor 118 or LMS unit 234 computesfeed forward equalizer coefficients 278 and decision feedback equalizercoefficients 280 and stores the computed coefficients in a memory suchas memory 120. In an example, feed forward equalizer coefficients 278and decision feedback equalizer coefficients 280 for multiple EMIfrequency bins may be computed and stored as shown in table 1 above. Inan alternate embodiment, step 602 is an optional step and feed forwardequalizer coefficients 278 and decision feedback equalizer coefficients280 are generated in real time by processor 118 or LMS unit 234.

In step 604, electromagnetic interference is detected in a receivedsignal. For example, a power spectral density spike 414 as seen in FIG.4B may be detected by tone detector 302. In an alternate example, errorsin decoded output 268 of LDPC decoder 216 or a Cyclic Redundancy Check(CRC) error may be used to detect EMI. In a further example, aSignal-to-Noise Ratio (SNR) and/or a sudden drop in SNR may be used todetect EMI.

In step 605, all adaptive filters as well as timing recovery integralloops may be stalled or frozen and released or re-started after DFEcoefficients are exchanged in order to speed up the convergence ofadaptive filters

In step 606, a frequency of the EMI detected in step 604 is determined.For example, tone detector 302 may detect a frequency 406 of EMI spike414.

In step 608, feed forward equalizer coefficients and decision feedbackequalizer coefficients are selected or computed corresponding to thefrequency of EMI determined in step 606. In an example, LMS unit 234computes feed forward equalizer coefficients and the decision feedbackequalizer coefficients are selected from the table that is determined instep 602. In an alternative embodiment, processor 118 selects feedforward equalizer coefficients and decision feedback equalizercoefficients determined in step 602 based on the detected frequency instep 606. In an alternate embodiment, feed forward equalizercoefficients and decision feedback equalizer coefficients are computedin real time by processor 118 or LMS unit 234.

In step 610, the feed forward equalizer coefficients selected in step608 are applied to the feed forward equalizer so as to substantiallyeliminate effects of the EMI from the received signal. For example, feedforward equalizer coefficients 278 are applied to feed forward equalizer222 so as to modify a frequency response of feed forward equalizer 222by creating a notch, for example notch 416 in FIG. 4C at the frequency406 of the detected EMI.

In step 612, the presence of EMI is signaled to a link partner. Forexample, as described above, the direct digital frequency synthesizer310 may generate a signal 312 to indicate presence of EMI to a linkpartner. In an alternative embodiment, a sequence of bits in a pluralityof LDPC frames may be sent to the link partner to indicate presence ofEMI.

In step 614, DFE coefficients corresponding to the detected EMIfrequency and/or the EMI frequency may be sent to the link partner. Forexample, processor 118 of link 102 may send DFE coefficients computed instep 602 to a link partner in a HDLC frame. In another example, directdigital frequency synthesizer 310 may generate a sine wave signal 312 ofa frequency equal to the EMI frequency and transmit the signal 312 tothe link partner 104 to indicate the frequency of the EMI signal. Uponreceiving the DFE coefficients, the link partner 104 may apply thereceived filter coefficients to pre-coder 206 so as to compensate forthe notch created in the frequency response of feed forward equalizer222 by link 102. In another example, upon receiving signal 312indicating frequency of the detected EMI, the link partner may select aDFE coefficient from pre-stored DFE coefficients corresponding to thefrequency indicated by signal 312.

FIG. 7 illustrates an example flowchart 700 depicting steps performed bya PHY layer upon receiving indication of EMI from a link partner,according to an exemplary embodiment. Flowchart 700 will be describedwith continued reference to the example operating environment depictedin FIGS. 1-5. However, the flowchart is not limited to theseembodiments. Note that some steps shown in flowchart 700 do notnecessarily have to occur in the order shown.

In step 702, a signal indicating presence of EMI is received from a linkpartner. For example, as described above, a sequence of bits in multipleconsecutive of LDPC blocks may be received from a link partnerindicating presence of EMI. In another example, a sine wave may bereceived from a direct digital frequency synthesizer 310 indicatingpresence of EMI.

In step 704, DFE coefficients and/or the frequency of the detected EMImay be received. For example, DFE coefficients for pre-coder 206 may bereceived in a HDLC frame or in a LLDP frame from the link partner. In analternative embodiment, the frequency of the sine wave signal fromdirect digital frequency synthesizer 310 of the link partner mayindicate the frequency of the electromagnetic interference detected bythe link partner.

In step 705, FFE coefficients may be computed or looked up in a tablebased on the DFE coefficients and/or frequency of the EMI received instep 704. The FFE coefficients are applied to the FFE. For example, FFEcoefficients may be applied to FFE 278.

In step 706, DFE coefficients are applied to a pre-coder to compensatefor the effects of the notch in the feed forward equalizer of the linkpartner that sent the DFE coefficients in step 704. For example, DFEcoefficients received in step 704 are applied to pre-coder 206. In anembodiment, processor 118, based on the frequency received in step 704,computes DFE coefficients 280 and applies them to pre-coder 206. In analternative embodiment, based on the frequency received in step 704, LMSunit 234 computes DFE coefficients 280 in real time and applies the DFEcoefficients to pre-coder 206. In alternate embodiment, processor 118computes DFE coefficients 280 in real time and applies the DFEcoefficients to pre-coder 206.

Single Ended EMI Adaptation

In an alternate embodiment, a link 102 upon detecting EMI may adjust thefrequency response of its FFE 222, but not send DFE coefficients to thelink partner 104. Instead, link 102 may activate its own DFE 220 andapply DFE coefficients corresponding to the detected EMI frequency toDFE 220 to account for the adapted frequency response of FFE 222. Thisalternate embodiment may be used in the event a link partner 104 is madeby a different vendor than link 102, and hence does not implement theEMI elimination methods described herein. Steps performed in such anembodiment are described below with reference to FIG. 8.

FIG. 8 illustrates an example flowchart 800 that depicts steps performedby a PHY transceiver to substantially eliminate effect of EMI from areceived signal according to an exemplary embodiment. Flowchart 800 willbe described with continued reference to the example operatingenvironment in FIGS. 1-5. However, the flowchart is not limited to theseembodiments. Note that some of the steps in flowchart 800 do notnecessarily have to occur in the order shown.

In step 802, filter coefficients corresponding to multiple frequencybins of EMI are pre-computed and stored prior to the onset of EMI. Forexample, processor 118 or least means squared unit 234 computes feedforward equalizer coefficients 278 and decision feedback equalizercoefficients 280 for multiple EMI frequencies and stores the computedcoefficients in a memory such as memory 120. In an example, feed forwardequalizer coefficients 278 and decision feedback equalizer coefficients280 for multiple EMI frequency bins may be computed and stored as shownin Table 1 above. In an alternate embodiment, step 802 is an optionalstep and feed forward equalizer coefficients 278 and decision feedbackequalizer coefficients 280 are generated in real time by processor 118or LMS unit 234.

In step 804, electromagnetic interference is detected in a receivedsignal. For example, a power spectral density spike 414 as seen in FIG.4B may be detected by tone detector 302. For strong EMI signals, tonedetector 302 may detect EMI using digital signal 252. For moderatestrength EMI signals, tone detector 302 may detect EMI using adaptedsignal 260. For very weak EMI signals, tone detector 302 may detect theEMI using a difference between sliced signal 264 and slicer input signal263.

In step 806, a frequency of the EMI detected in step 804 is determined.For example, tone detector 302 may detect a frequency 406 of EMI spike414.

In step 808, feed forward equalizer coefficients and decision feedbackequalizer coefficients are selected corresponding to the frequency ofEMI determined in step 806. In an example, LMS unit 234 selects feedforward equalizer coefficients and decision feedback equalizercoefficients determined in step 802 for feed forward equalizer 222 anddecision feedback equalizer 220 based on the frequency of the EMIdetected in step 806. In an alternative embodiment, processor 118computes feed forward equalizer coefficients and decision feedbackequalizer coefficients determined in step 802 based on the detectedfrequency in step 806. The feed forward equalizer coefficients anddecision feedback equalizer coefficients may also be selected from Table1 above.

In step 810, the feed forward equalizer coefficients and decisionfeedback equalizer coefficients selected in step 808 are applied to feedforward equalizer 222 and decision feedback filter 220. For example, FFEcoefficients 278 and DFE coefficients 280 selected/determined in step808 are applied to feed forward equalizer 222 and decision feedbackequalizer 220 respectively. Conventionally, decision feedback equalizer220 is turned off after startup sequence. However, in this particularembodiment DFE coefficients 220 is turned on and no signal is sent tolink partner indicated presence of EMI.

Embodiments presented herein, or portions thereof, can be implemented inhardware, firmware, software, and/or combinations thereof.

The embodiments presented herein apply to any communication system thatmay experience the adverse effects of EMI, or to any communicationsystem where knowledge of the channel condition is known, or can beestimated at the transmitting or receiving side.

The representative signal processing functions described herein (e.g.part of whole of PHY 108′) can be implemented in hardware, software, orsome combination thereof. For instance, the signal processing functionscan be implemented using computer processors, such as processors 118,computer logic, application specific circuits (ASIC), digital signalprocessors, etc., as will be understood by those skilled in the artsbased on the discussion given herein. Accordingly, any processor thatperforms the signal processing functions described herein is within thescope and spirit of the embodiments presented herein.

Further, the signal processing functions described herein could beembodied by computer program instructions that are executed by acomputer processor, for example processors 118, or any one of thehardware devices listed above. The computer program instructions causethe processor to perform the signal processing functions describedherein. The computer program instructions (e.g. software) can be storedin a computer usable medium, computer program medium, or any storagemedium that can be accessed by a computer or processor. Such mediainclude a memory device, such as memory 120, a RAM or ROM, or other typeof computer storage medium such as a computer disk or CD ROM, or theequivalent. Accordingly, any computer storage medium having computerprogram code that cause a processor to perform the signal processingfunctions described herein are within the scope and spirit of theembodiments presented herein.

CONCLUSION

While various embodiments have been described above, it should beunderstood that they have been presented by way of example, and notlimitation. It will be apparent to persons skilled in the relevant artthat various changes in form and detail can be made therein withoutdeparting from the spirit and scope of the embodiments presented herein.

The embodiments presented herein have been described above with the aidof functional building blocks and method steps illustrating theperformance of specified functions and relationships thereof. Theboundaries of these functional building blocks and method steps havebeen arbitrarily defined herein for the convenience of the description.Alternate boundaries can be defined so long as the specified functionsand relationships thereof are appropriately performed. Any suchalternate boundaries are thus within the scope and spirit of the claimedembodiments. One skilled in the art will recognize that these functionalbuilding blocks can be implemented by discrete components, applicationspecific integrated circuits, processors executing appropriate softwareand the like or any combination thereof. Thus, the breadth and scope ofthe present embodiments should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with the following claims and their equivalents.

1. A method to substantially eliminate effects of EMI in an Ethernetsystem, comprising: computing and storing filter coefficientscorresponding to a range of EMI frequencies; receiving a signal;detecting EMI in the received signal; determining a frequency of thedetected EMI; selecting filter coefficients corresponding to thedetermined frequency of the EMI; and adjusting a frequency response ofone or more filters using the selected filter coefficients so as tosubstantially eliminate effects of EMI in the received signal.
 2. Themethod of claim 1 further comprising signaling presence of EMI to a linkpartner.
 3. The method of claim 2, the signaling step comprising sendinga predetermined sequence of bits in a plurality of consecutive frames toindicate the presence of EMI to the link partner.
 4. The method of claim3, further comprising sending the predetermined sequence of bits usingauxiliary bits.
 5. The method of claim 1, further comprising signalingpresence of the EMI to a link partner by transmitting a sine wave equalin frequency to that of the detected EMI.
 6. The method of claim 1,further comprising signaling presence of the EMI to a link partner bytransmitting a sine wave based on a frequency of the detected EMI. 7.The method of claim 1, further comprising sending decision feedbackequalizer filter coefficients corresponding to the frequency of the EMIto the link partner.
 8. The method of claim 6, further comprisingsending decision feedback equalizer filter coefficients by encoding thedecision feedback filter coefficients in a High-level Data Link Control(HDLC) packet.
 9. The method of claim 1, further comprising sending afrequency of the detected EMI to the link partner by encoding thefrequency in a High-level Data Link Control (HDLC) packet.
 10. Themethod of claim 1, the detecting step comprising distinguishing the EMIfrom the received signal by using the Power Spectral Density (PSD) ofthe received signal.
 11. The method of claim 1, the detecting stepcomprising detecting the EMI based on an output of an analog-to-digitalconverter.
 12. The method of claim 1, the detecting step comprisingdetecting the EMI based on an input to a Feed Forward Equalizer (FFE).13. The method of claim 1, the detecting step comprising detecting theEMI based on a difference between an output of a slicer and an input ofthe slicer.
 14. The method of claim 1, the determining step comprisingdetermining the frequency of the EMI based on one or more of an outputof an analog-to-digital converter, an input to a Feed Forward Equalizer(FFE) and an output of a slicer.
 15. The method of claim 1, furthercomprising performing the detecting, determining, selecting andadjusting steps in less than a pre-determined amount of time.
 16. Themethod of claim 15, wherein the pre-determined amount of time is 10 ms.17. The method of claim 1, wherein the filter coefficients are for aFeed Forward Equalizer and a Decision Feedback Equalizer.
 18. The methodof claim 1, wherein the filter coefficients are for a notch filter. 19.A system to substantially eliminate effects of EMI burst noise in anEthernet system, comprising: at least one of a Least-mean-square (LMS)module and a processor configured to compute and store filtercoefficients corresponding to a range of pre-determined EMI frequencies;a tone detector configured to detect EMI in a received signal anddetermine a frequency of the detected EMI; a Feed Forward Equalizer(FFE) configured to adapt its frequency response using filtercoefficients corresponding to the frequency of the detected EMI so as tosubstantially eliminate the effects of EMI in the received signal; and aDecision Feedback Equalizer (FFE) configured to adapt its frequencyresponse using filter coefficients corresponding to the frequency of thedetected EMI so as to substantially eliminate the effects of EMI in thereceived signal.
 20. The system of claim 19, further comprising aprocessor configured to signal presence of EMI to a link partner bysending a predetermined sequence of auxiliary bits in a plurality ofLDPC blocks.
 21. The system of claim 19, further comprising a DirectDigital Frequency Synthesizer (DDFS) configured to signal presence ofthe EMI to a link partner by sending the link-partner a sine wave equalin magnitude and frequency to that of the detected EMI.
 22. The systemof claim 19, further comprising a processor configured to transmitfilter coefficients corresponding to the frequency of the EMI to thelink partner by encoding the filter coefficients in an High-level DataLink Control (HDLC) packet.
 23. The system of claim 19, furthercomprising a processor configured to transmit a frequency of thedetected EMI to the link partner by encoding the frequency in anHigh-level Data Link Control (HDLC) packet.
 24. The system of claim 19,wherein the tone detector is configured to detect the EMI and thefrequency of the EMI based on an output of an analog-to-digitalconverter.
 25. The system of claim 19, wherein the tone detector isconfigured to detect the EMI and the frequency of the EMI based on aninput to the Feed Forward Equalizer.
 26. The system of claim 19, whereinthe tone detector is configured to detect the EMI and the frequency ofthe EMI based on an output of a slicer.
 27. The system of claim 19,wherein the Feed Forward Equalizer includes a configurable notch filterenabled to remove the EMI at the detected frequency.
 28. The system ofclaim 19, wherein the processor is configured to select filtercoefficients corresponding to the determined frequency of the detectedEMI.
 29. A method to reduce effects of EMI burst noise in an Ethernetsystem, comprising: receiving a signal from a link partner indicatingpresence of EMI; receiving filter coefficients for a programmablepre-coder from the link partner corresponding to a detected frequency ofthe EMI signal; and adjusting a frequency response of the pre-coderusing the received filter coefficients so as to substantially eliminateeffects of the EMI on the received signal.
 30. The system of claim 29,wherein the programmable pre-coder is a Tomlinson-Harashima pre-coder.31. A computer readable medium having stored thereon computer executableinstructions that, if executed by a computing device, cause thecomputing device to perform a method comprising: computing and storingfilter coefficients corresponding to a range of EMI frequencies;receiving a signal indicating presence of EMI and a frequency of theEMI; selecting filter coefficients corresponding to the determinedfrequency of the EMI; and adjusting a frequency response of one or morefilters using the selected filter coefficients so as to substantiallyeliminate effects of EMI in the received signal.